The present invention relates to an image display system composed of an input device such as a keyboard or a mouse, a computer, and a display device. More specifically, the present invention relates to an image display system that is capable of adjusting position of an image in the horizontal and vertical directions.
Display devices used as a terminal for a computer vary in screen size and deflection frequency of a video signal to be displayed. With this respect, such display devices have been used that support various types of video signals. Some of these display devices provide optimum screen images for individual video signals by means of using a microcomputer and/or a memory LSI.
A first prior art is disclosed in Japanese Patent Laid-open No. 1-321475. An image display system according to the first prior art comprises a memory that stores image display position information and display size information for each image signal. The memory is controlled by, for example, a microcomputer. More specifically, the microcomputer reads out of the memory the image display position information and the display size information, as read-out information, that are optimum for an incoming video signal and controls a component or components such as a deflection circuit for the display device in accordance with the read-out information.
On the other hand, the incoming video signal to the display device may have an unknown type. The memory stores no information about such an unknown video signal. Under such circumstances, adjustment buttons on, for example, a front surface of the display device are used to input information for adjusting the image display position and the screen size. The microcomputer produces control information for deflection and others based on the adjustment information supplied and performs adjustment.
A second prior art is disclosed in Japanese Patent Laid-open No. 5-232918. The second prior art produces a control signal for a display device with the control signal being superposed on a video signal or a synchronization signal. The display device comprises a control signal extraction circuit and a control circuit. The extraction circuit extracts the control signal superposed on the video signal or the synchronization signal. The control circuit adjusts a video circuit or a deflection circuit in accordance with an extracted control signal.
Various methods including the above-mentioned first and second prior arts have been known for adjusting a typical display device and examples include methods for displaying an on-screen adjustment menu on the screen and methods for displaying an adjustment menu as an application program on an operation system. These adjustment menu requires an operator to depress a certain button or buttons on the front surface of the display device or to click a certain icon designated by the application program with a mouse pointer for the adjustment.
In the first prior art, controls of the image display position and the screen size are all managed by the display device itself. An operator should leave his or her hand from the input device such as a keyboard or a mouse connected to the computer and touch the adjustment button on the display device for adjustment, if required. This is often an onerous operation.
The second prior art allows operation of the display device with the input device such as a keyboard connected to the computer. However, such control with the keyboard requires combination of alphanumeric character keys to enter a command. Therefore, commanding operation with the keyboard is somewhat onerous and takes a relatively long time for proper control of the display device.
Display devices that support display of a typical adjustment menu permit only the adjustment in a single direction at a time such as in the horizontal or the vertical direction. The adjustment in one direction follows the additional adjustment in the other direction, which takes a relatively long time.
Furthermore, a control circuit for image adjustment should be provided in the computer for the adjustment of the image display system with the input device such as a keyboard or a mouse. Such a circuit complicates the configuration of the entire system.